1. Field of the Invention
This invention relates to a method of treating a so-called super-high strength nylon cord having a yarn strength of not less than 12 g/d with an adhesive.
2. Related Art Statement
Nylon fibers have excellent strength, durability and heat resistance among cord materials for tire reinforcement, so that they are frequently applied to large size tires for truck, bus, construction vehicle, airplane and the like.
On the other hand, it is strongly demanded to reduce the laminating number of reinforcing materials in the tire as well as the end count of cords in the reinforcing material from viewpoints of cost down, low fuel consumption owing to reduction of tire weight, resource-saving and the like.
For such demands, nylon fibers having a molecular weight equal to that of the conventional nylon and considerably increasing the strength have recently been developed (for example, Japanese Patent laid open No. 59-26517 and No. 61-70008), from which there is a possibility of developing a strength of not less than 12 g/d. However, the inventors have confirmed that such a nylon having higher strength (hereinafter referred to as a super-high strength nylon) has a drawback that the strength is largely lowered after the adhesive treatment (hereinafter referred to as dipping) and the strength of the resulting dipped cord is approximately equal to that of the conventional nylon.
Moreover, the some reduction of strength is caused even in the dipping of the high strength nylon having a yarn strength of about 10.5 g/d. In this connection, various dipping systems are proposed as a countermeasure for preventing the strength reduction of such a dipped cord (Japanese Patent laid open No. 60-71238, No. 60-71239 and No. 60-71240). However, all of these countermeasures are applied to only the high strength nylon having a yarn strength of about 10.5 g/d. Up to the present, there is not yet developed a method of preventing the reduction of strength in the super-high strength nylon aimed at the invention.
Under the above circumstances, the inventors have made various studies in order to develop a method for the prevention of strength reduction in the super-high strength nylon and found that the reduction of strength in the dipped cord made from the super-high strength nylon having a yarn strength of not less than 12 g/d can be prevented by rendering a tension of the cord into not less than 0.5 g/d in the dipping solution or by preliminarily treating the cord at a temperature of not lower than 100.degree. C. when the tire reinforcing cords made from super-high strength nylon-6 or nylon-6,6 fibers having a yarn strength of not less than 12 g/d are subjected to a dipping treatment with a mixed solution of resorcin-formaldehyde condensate and rubber latex (Japanese Patent Application No. 62-32526).
According to such a dipping method, the reduction of strength in the dipped cord is certainly prevented, but the adhesion force is fairly low. As a result, when such a dipped cord is used as a tire reinforcing cord, there is a serious problem that the adhesion force between rubber and cord is considerably poor.